I tried to slow play KK in position, and I think perhaps this was a mistake.

Any suggestions on how to better play this hand?

Full Tilt No-Limit Hold'em, $0.05 BB (9 handed) - Full-Tilt Converter Tool from FlopTurnRiver.com
MP1 ($2.02)
MP2 ($5.02)
MP3 ($5)
CO ($5)
Button ($6.10)
SB ($5.52)
Hero (BB) ($3)
UTG ($3.60)
UTG+1 ($2.20)
Preflop: Hero is BB with K, K
7 folds, SB calls $0.03, Hero checks
Flop: ($0.10) 8, 9, 4 (2 players)
SB bets $0.05, Hero raises to $0.20, SB calls $0.15
Turn: ($0.50) 9 (2 players)
SB checks, Hero checks
River: ($0.50) 8 (2 players)
SB bets $0.20, Hero folds
Total pot: $0.50 | Rake: $0.03

You're right, it is a mistake to not raise. We want to get value out of our good hands to beat blinds+rake(+badluck). We stand to profit from the range he limp/calls with, not the range he limp/folds (as he just is going to fold this on the flop unless he hits a miracle hand). Also, by raising preflop we reduce the possible range he can have postflop, making it easier to handread.

yeah, I decided that he was on either an 8 or 9, because when I reraised him on the he called. I can't see him calling with no pair. Raise preflop win a small pot, limp and loose a larger one.

Do you think 3xBB is appropriate or should I go for a different amount to extract the most knowledge and value

Turn and River are really lame cards :/

I follow the general guide of 3x+1/limper in position and 4x+1/limper OOP (For cash games). Sometimes you can bet more or less depending on the situation

Raise pre.